Researchers have come to examine shoulder bones of humans in order to search for the earliest common ancestor between apes and humans before early humans learned to walk, from the treetops of the savannas in Africa.
Researchers from the University of California, San Francisco suggest that the last common ancestor of humans and apes appear closely to modern chimpanzees along with their behavior as well, as opposed to modern humans. However, scientists still have an unclear idea what this ancestor look like in appearance.
According to the lead author of the study, Nathan Young from UCSF, humans possess features that are clearly linked to African apes however, we also have features that are more primitive, that can lead to any clues how this common ancestor once looked like.
He adds that the most plausible explanation is that this ancestor most likely resembles a chimp or a gorilla upon closer inspection of the shoulders. This shift in shoulder shape reveals evidence of how early humans adapted new behaviors like lesser time spent climbing trees and the crucial use of tools.
Modern African apes possess shoulders with a trowel shaped blade and spine curved like a handle for easier movement and upswing of the arm above the skull, to gain a better advantage in climbing trees and swinging along branches. In modern monkeys and humans, the shoulder joint is slighted more downwards which is clear evidence of behavior caused by tool making and throwing objects for hunting such as spears in high speed.
Human lineage apparently diverted from chimps, who are our closest living relatives, some 6 to 7 million years ago.
Since fossil evidence of the earliest common ancestor is difficult to retrieve, researchers now use 3D models of shoulders from museum specimens of early hominids, modern humans and chimps, along with gorillas, gibbons, monkeys and even orangutans.
The specimens were then analyzed with two early Australopithecus hominid species called the primitive A. afarensis and the younger A. sediba. The results revealed that A. afarensis is more African ape-like than human where A. Sediba closely resembles human shoulders than apes'.
According to senior anthropology curator, Zeray Alemseged of the California Academy of Sciences, this mix of ape and human features found in A. afarensis' shoulder suggests that even if it is bipedal, the species also engaged in tree climbing activity and also produced stone tools. This primitive species showed that it is slowly evolving into a human.
Young agrees with this assessment where he says that the australopithecines were prime intermediate forms of African apes and modern humans, presenting a gradual shift from trees to an increasing reliance on tools, which is the driving force of early evolution in humans.
This new study is published in the journal, PNAS.